cracked trans housing
www.wittrans.com has them ranging in price from $39-$60. Here's a direct link to the page with all the various versions of 904's made
https://www.wittrans.com/SchematicParts.aspx?Transmission=A904&LinkCode=760
Just pick the year case and for what engine (small block or /6).
The bellhousing is a high stress area since engine torque twists on it right there. Unless it was for a tired 170 slant 6 I wouldn't bother welding one up. Sure would suck to go through all the work of welding it up, rebuilding it, installing it then having it crack again a couple thousand miles down the road.